For those of you following at home :-), the solution is below:
The i12+ & PCEye Mini, with TGIS installed, do not have a ‘Tobii Engine’ running. Therefore if you call tobii_engine_create, it fails. If Windows Control 2 is installed, ‘Tobii Engine’ comes along with it and it works.
It turns out there are two ways to enumerate Tobii devices through the SDK, one uses the engine (tobii_enumerate_devices) and one enumerates them directly (tobii_enumerate_local_device_urls). You need to detect if the tobii_engine is running or not and change which API call you make.
– Jay